Van type vehicles for passengers and for cargo are frequently equipped with sliding side doors. Many vans include a single sliding door on the passenger side of the van. However, the van may be equipped with sliding doors on both sides. Drivers and passengers can open or close sliding doors of this type manually from inside or outside of the vehicle. However, the sliding door is usually heavy and often inconvenient and/or difficult to move manually, particularly from inside the vehicle.
For convenience, power operated sliding door closure systems have been developed to allow drivers and passengers to open and close a sliding door virtually effortlessly. Moreover the sliding door usually can be opened or closed from the driver's seat and/or one or more other locations remote from the sliding door.
One type of power operated sliding door closure system, known as a “closed loop” system, is disclosed in U.S. Pat. No. 5,396,158 which issued Mar. 7, 1995 to Joseph D. Long et al. The Long et al. '158 patent discloses a power operated sliding door closure system in which a sliding door is mounted on a van by travelers that are slidably supported in upper, center and lower tracks. An opening and closing module is mounted inside the van adjacent the center track. A front cable is attached to a front cable drive pulley or drum and extends from the front drum to the traveler through a front cable roller guide assembly. A rear cable is attached to a rear cable drive pulley or drum and extends from the rear drum to the traveler through a rear cable roller guide assembly. The front and rear cable drive drums each have a large diameter helical cable groove.
A motor drive unit rotates the front and rear cable drive drums to move the sliding door. The motor drive unit, as best shown in FIG. 3 of the Long et al. '158 patent, comprises an electric motor that drives a drive gear that is coaxially aligned with the front and rear cable drive drums. A coil spring is seated in an annular opening in the cable drive drums. An upper spring end is anchored on the rear cable drive drum and a lower spring end is anchored on the front cable drive drum. The coil spring is a tension retaining spring that urges the front cable drive drum in the counterclockwise winding direction and the rear cable drive spool in the opposite clockwise winding direction so that the front and rear cables are maintained in tension at all times.
While the “closed loop” type of system disclosed in the Long et al. '158 patent is satisfactory for its intended purpose, assembly of the system may be difficult because of the tension retaining spring that takes up slack and insures that the front and rear cables are maintained in tension at all times. Considerable slack is often desired to facilitate assembly of the closed loop system because the traveler (roller hinge assembly shown at 26 in the Long et al. '158 patent) must be inserted into the track (usually the center track shown at 18 in the Long et al. '158 patent) after the ends of the front and rear cables are attached to the traveler. However, the coil spring in the system noted above, must be tensioned or wound up to provide any slack at all and even then the slack may not be enough to facilitate insertion of the traveler into one end of the track. Furthermore even with sufficient slack, the cables may not position the traveler correctly for insertion into the one end of the track.
Another way to take up slack in a “closed loop” system is disclosed in the U.S. Pat. Nos. 5,319,880 and 5,319,881 granted to Howard W. Kuhlman Jun. 14, 1994. These patents disclose a mechanical take-up device comprising a small cable slack take-up pulley 174 and a cooperating tooth rack 172 mounted on the cable pulley. One end of one of the cables is attached to the small cable slack take-up pulley. After both cables are attached to the traveler and the traveler is inserted into the track, the cable slack is taken up by rotating the small cable slack take-up pulley with a special tool. See also pending patent application Ser. No. 09/970,167 filed Oct. 3, 2001. The mechanical take up device facilitates assembly by allowing sufficient slack in the cables. However, the cables still may not position the traveler correctly. Moreover, the take-up device is complicated and expensive and requires a special tool for operation.